Currently, in the wireless communication system, a technology in which the user equipment simultaneously performs wireless data connections with a plurality of base stations over different carriers has been widely applied. However, in some cases, such as cases in which wireless link failure occurs between the user equipment and a certain base station, it needs to share load for a certain base station, a primary carrier signal quality between the user equipment and a certain base station is low or the like, it might need to release the wireless data connection between the user equipment and the base station and/or transfer part or all of the data bearers with regard to this base station to other base station.